1. Field of the Invention
This invention relates to aerosol dispensers and packaged aerosol compositions which are suitable for topical use. In particular, it relates to aspects of the aerosol hardware which makes the dispenser particularly suitable for spraying aerosol compositions which contain particulate material, and to topical compositions containing particulate material for packaging therein.
2. The Related Art
It has long been appreciated that a problem with spraying topical compositions containing particulate material is that there is a tendency for such aerosol products to suffer excessive nozzle blockage. This results in the user being unable to discharge the product from the aerosol container fully, with the result that the user is often left with some product in the container they are unable to dispense.
A variety of solutions have been adopted to overcome this problem, some involving modification of the aerosol hardware, whilst others have involved modification of the formulation being sprayed. For example, GB 2 029 441 describes a powder aerosol composition comprising a suspension of 5 to 60% by weight of powder, 5 to 80% of short chain alcohol and 5 to 80% water, together with 5 to 40% propellant having a specific gravity lower than the suspension. This composition is said to be designed to facilitate redispersion, and therefore minimise the rate of agglomeration and nozzle clogging.
CA 1 106 329 addresses the same technical problem specifically in the field of suspension antiperspirant compositions, and alleges to overcome it by providing a suspension aerosol system incorporating a large amount of powdered antiperspirant active distributed in a substantially anhydrous oil system, which in turn is suspended in relatively small quantities of propellant. This composition in turn is dispensed from an aerosol container having a metered valve, which delivers uniform dosages of antiperspirant composition in use.
It has also been observed that any problems observed with blockage in a powder aerosol product tend to be exaggerated if the spray rate is relatively low. Typical spray rates for powder aerosols are in the region 0.7-1.2 gs.sup.-1 at 25.degree. C. We have found the problem to be particularly acute if the spray rate is taken below this, for example to levels in the region 0.25-0.6 gs.sup.-1 at 25.degree. C. The problems are also exaggerated if the solids content of the spray composition is high; that is if the composition (inclusive of propellant) contains more than about 4% suspended solids, in particular more than about 10% suspended solids.
From our detailed study of trying to improve the spray characteristics of powder compositions, particularly with a view to decreasing the rate of blockage suffered by powder aerosols, we have found that certain hardware aspects of the aerosol dispenser are important in minimising the blockage rate.
A typical aerosol dispenser comprises a diptube which is attached to a valve assembly by means of a restricted tail piece. The valve assembly typically has one or more vapour phase taps, which permit propellant gas to enter the valve assembly, where it mixes with the composition to be sprayed, which is delivered to the valve assembly by the diptube. The valve assembly also typically has a generally open end, which is generally sealed by a gasket and a closure piece on the stem, which seals the orifice in the gasket. The closure piece on the stem is generally biased to the closed position by the action of a spring located within the valve assembly.
Above the closure piece on the stem are one or more stem orifices, which are located generally towards the bottom of the stem. When the valve is not in use, these stem orifices are not in fluid communication with the valve assembly. The stem leads generally to an actuator button, which itself typically has an input orifice for the stem, an inner actuator chamber, and a terminal orifice through which sprayed fluid exits when the aerosol container is used.
In use, pressure by the user on the top of the actuator button causes the stem to depress. The closure piece of the stem acts on and compresses the spring in the valve assembly. Depression of the stem brings the stem orifice(s) into liquid contact with the valve assembly, whereby a mixture of gaseous propellant and liquid to be sprayed is driven through the stem orifice(s) and up the stem. The mixture subsequently enters the inner actuator chamber, and then exits the actuator via the terminal orifice.